This invention relates to an ultrasonic imaging apparatus and, in particular, to an ultrasonic imaging apparatus for use in medical diagnosis.
An ultrasonic imaging apparatus is known which is adapted to scan a human subject with an ultrasonic beam emitted from an ultrasonic transducer, comprised of an array of ultrasonic transducer elements, to process the echo signals obtained and to display them, as a tomographic image, on the screen of a monitor. This type of ultrasonic imaging apparatus is utilized as an ultrasonic diagnosis apparatus in the practice of medicine.
In the aforementioned ultrasonic imaging apparatus, since the time taken from the transmission of the ultrasonic wave to the reception of echo signals is necessarily above a given value due to the speed of sound travelling through the living body, a requisite time of one cycle including a dwell time from one transmission/reception cycle to the next transmission becomes considerably longer, placing an inherent limitation on the obtainment of a tomographic image in real time. In order to effectively utilize the requisite time of one cycle, two reception circuits are provided in a parallel fashion so that two kinds of reception signals are obtained from a single ultrasonic transmission so as to substantially form a double scanning line. This type of apparatus is disclosed, for example, in Japanese Patent Publication (KOKOKU) No. 56-20017.
With this method, two sound waves, each corresponding to a composition of one-direction transmission sound field and each of two reception sound fields, are detected as two echo waves. As the distance of the two reception beams becomes greater, both sound fields are displaced in a different direction, thus leading to a lowering in their reception sensitivity and a variation in their beam widths.